PROCESS OF PREPARING 2,3,5-TRIHALOBENZALDEHYDE

Abstract: A process of preparing 2,3,5-trihalobenzaldehyde, which comprises the steps of (i) reacting a compound of formula (I), wherein Hal is halogen, with a di-C1-4 alkylformamide; (ii) allowing the resulting complex to rearrange; and (iii) quenching the rearranged complex with water.

Description: PROCESS OF PREPARING 2,3,5 - TRIHALOBENZALDEHYDE The present invention relates to a novel process of preparing 2,3,5-trihalobenzaldehyde which is a useful starting material in the preparation of a number of pharmaceutical products. EP-A-0372934 and EP-A- 0459819 describe classes of 5-phenylpyrimidines that are potent inhibitors of glutamate release. Preferred examples are those wherein the phenyl ring is substituted in the 2,3,5- positions by halogen, especially chloro. Particular examples include 4-amino-2-(4-methylpiperazin-l-yl)-5-(2,3,5-trichlorophenyl) pyrimidine and 4-ammo-2-(4-n-propylpipera2-in-l-yl)-5-(2,3,5- trichlorophenyl) pyrimidine. Such 5-phenylpyrimidines are of utility in the treatment of cerebral ischaemic damage including particularly that resulting from stroke and head injury. The chemical synthesis of the preferred examples of 5-phenylpyrimidines, i.e. those wherein the phenyl ring is substituted in the 2,3,5- positions by halogen, generally requires the use of the correspondingly substituted benzaldehyde as the starting material. This benzaldehyde may generally be prepared in turn from sodium 3-amino-2,5- dihalobenzoate. For example, it is known to prepare the 2,3,5 trichlorobenzaldehyde from sodium-3-amino-2, 5-dichlorobenzoate via a Sandmeyer reaction and a DibalH reduction step as shown below: (i) NaNO 2 , conc H 2 SO4,ArOH (ϋ) CuCl,conc HCl (iϋ) MeOH, cone H2SO4 catalyst (iv) DIBALH -70°C (see standard organic chemistry textbooks, for example: J.March, Advanced Organic Chemistry Reactions, Mechanism and Structure, 4th Ed. (1992), pp 723 and Muraki and Mukaiyama, Chem. Lett.. 1974, 1447; 1975, 212). The disadvantages of this process are that the starting material itself is only available in limited quantities and in relatively impure form and that the DibalH reduction step is often low yielding. It has now been found that 2, 3, 5 trihalobenzaldehyde can be prepared from 1, 2, 4 trihalobenzene via a complex intermediate. The advantages of this process are that 1, 2, 4 trihalobenzene is readily available and the reaction is relatively simple and straightforward. Accordingly, the present invention provides a process of preparing 2, 3, 5- trihalobenzaldehyde, which comprises the steps of (i) reacting a compound of formula (I) : wherein Hal is halogen, with a di-Cι.4 alkyformamide; (ϋ) allowing the resulting complex to rearrange; and (iii) quenching the rearranged complex with water Examples of halogen include chloro. A preferred example of a di-Cι- alkylformamide is dimethylformamide (DMF). Preferably, the reaction between a compound of formula (I) and a di-Cι_4 alkylformamide is carried out at a reduced temperature to avoid tarring. Conveniently, this may be at a temperature from -20°C to -80°C, such as -60°C. Although not wishing to be bound in any way, it is believed that the complex resulting from the reaction between a compound of formula (I) and a di-C]_4 alkylformamide is of formula (II): wherein Hal is halogen. If the complex of formula (II) is quenched immediately with water, it will result in 2, 3, 6-trihalobenzaldehyde exclusively. If however, the complex is left for more than, say, 2 or 3 hours (say 2 to 24 hours) at or about room temperature (for example from 15°C t0 35°C), it rearranges into a further complex that is believed to be of formula (in): wherein Hal is halogen. If the complex of formula (III) is then quenched with water, 2, 3, 5- trihalobenzaldehyde is produced. The latter may optionally be reduced by, for example, sodium borohydride to form the corresponding 2, 3, 5-trihalobenzyl alcohol for further processing should such be required. The rearrangement of the complex of formula (II), is quite unexpected from the prior art, especially Synthesis Communication, October 1988 (p803). T.H. Kress and M.R. Leanna. This prior art provides no indication at all that, if the complex is left, it will rearrange in this way. The compound of formula (I) may in turn be obtained by reacting a 1, 2, 4- trihalobenzene with a C\. alkyllithium in a cyclic or open-chain ether solvent at a reduced temperature preferably below -20°C, and most preferably below -60°C. The preferred C ] _6 alkyllithium has a straight carbon chain with methyllithium or n- butyllithium being the most preferred. Preferably, the cyclic or open chained ether solvent is diethyl ether or THF. When the molar ratio of C\. alkyllithium : di C1-.4 alkyl formamide is 1 : 2.55, the overall yield of 2, 3, 5 trihalobenzaldehyde is approximately 35% at approximately 95% purity. Surprisingly, it was found that a ratio of 1 : 5.45 of C1--.4 alkyllithium : di C1--.4 alkylformamide gave the very much increased yield of 70%, at 95% purity. The following examples are provided by way of illustration of the present invention and should not be construed in any way as constituting a limitation thereof. Example 1 (a) Preparation of 2. 3. 5-trichlorobenzaldehyde H 2 0 Reagents 1, 2, 4-Trichlorobenzene 18.14g 0.10 mole THF (dry) (tetrahydrofuran) 250ml;50ml;50ml n-butyllithium 2.5M in hexane 44ml 0.11 mole DMF (dry) 20.23g. 0.28 mole Water 5ml Saturated aqueous sodium chloride solution 400ml Ethylacetate 2 x 200 ml Dry THF (250ml) was stirred under nitrogen while cooling in an SVM dry ice bath. A 2.5 molar solution of n-butyllithium in hexane (44ml,0.11 mole) was added dropwise keeping the temperature below -60°C. A solution of 1, 2, 4-trichlorobenzene (18.14g,0.10 mole) in dry THF (50ml) was then added dropwise keeping the temperature below -60°C. The resulting mixture was stirred for 30 min at -65°C to -60° C. To the latter, a solution of dry dimethylformamide (20.23g, 0.28 mole) in dry THF (50ml) was then added dropwise keeping the reaction temperature below -60°C. The reaction mixture was allowed to warm to room temperature and left to stand overnight. Water (5ml) was added and the mixture was stirred for 15 min. The mixture was then poured into sat. sodium chloride solution (400ml). After stirring the latter for 10 mins, the two phases were separated and the aqueous phase extracted with ethyl acetate (2 x 200ml). The combined organic extracts were dried over anhydrous magnesium sulphate, and concentrated under reduced pressure to a golden oil (26.6g). (b) Preparation of 2.3.5-Trichlorobenaldehyde Reagents 1 ,2,4-Trichlorobenzene 362.9g 2.0 mole THF (dry) 3270ml Butyllithium (2.5M in hexane) 923ml 2.3 mole DMF (dry) 804. lg 11.0 mole A solution of 1,2,4-trichlorobenzene (362.9g, 2.0 mole) in dry THF (3270ml) was stirred whilst cooling in an acetone/dry ice bath. A 2.5 molar solution of butyllithium in hexane (923ml, 2.3 mole) was added dropwise keeping the temperature below -60°C. After stirring for 10 minutes, dry dimethylformadide (804. lg, 11.0 mole) was added dropwise below -60°C. The reaction mixture was stirred for 18 hours whilst warming to ambient temperature. Water (3000ml) was added and the mixture was stirred for 15min. The mixture was then poured into sat. sodium chloride solution (400ml). After stirring the latter for 10 mins, the two phases were separated and the aqueous phase extracted with ethyl acetate (2 x 3000ml). The combined organic extracts were dried over anhydrous magnesium sulphate, and concentrated under reduced pressure to a golden oil (292g). Example 2 Preparation of N-methylpiperazinoformamidine hydriodide Thiourea (10.8g) was dissolved in acetone (250ml) at 50°C. Iodomethane (10ml) was added and the reaction was stirred at 50°C for 4 hours. After cooling, the solution was diluted with ether (1 litre) and the methiodide salt was filtered, washed with ether and dried in vacuo. 29.2g, mp. 113-115°C. The methiodide salt (5g) was dissolved in water (30ml) and N-methylpiperazine was added. The solution was stirred, with nitrogen bubbled through, at room temperature for 24 hours. The solution was concentrated in vacuo. The residue was sluπied with ethanol, filtered and dried in vacuo. 4.98g, mp. 230-242°C. Example 3 (i) Preparation of 2.3.4-trichlorobenzylalcohol To a solution of 2,3,5-trichlorobenzaldehyde (Aldrich, 50gms) in ethanol (1.0 1) at room temperature was added aBH4 (7.00gms) and the resulting mixture stirred for 3.5 hours. The reaction was quenched with water and the solvent evaporated in vacuo before partitioning the residue between CHCI3 and saturated NaHCO3 solution. The organic phase was washed with brine, dried over MgSO4, filtered and the solvent evaporated in vacuo to leave a white solid, 43.00gms, mp. 90-93°C. (ϋ) Preparation of 2.3.5-trichlorobenzyl bromide To a solution of the alcohol in benzene (400 ml) under N 2 was added PBr3 (126.48gms) and the mixture stirred at 55-60°C for 3.5 hours. After cooling, the mixture was poured onto crushed ice (2 1) and the benzene layer separated. The aqueous phase was washed with benzene (x3) and the combined benzene extracts washed with saturated NaHCO3 solution and water, dried over MgSO4, filtered and the solvent evaporated to leave a brownish liquid which solidified on standing, 37.53gms, mp. 40-42°C. (iii) Preparation of 2.3.5 -trichlorophenylacetonitrile The bromide was suspended in dimethylformamide (DMF) (130ml)/water (86.67ml) at 0°C and KCN (12.99gms) added in portions. After stirring at 30-35°C for 3 hours, the suspension was diluted with water and extracted with diethyl ether (Et2θ). The combined ether extracts were washed with water, dried over MgSO4, filtered and the solvent evaporated in vacuo. Chromatography on silica gel eluting with hexane to 20% ether-hexane gave the desired product as a white solid, 18.52gms, mp. 60-62°C. (iv) Preparation of 2-f2.3.5-tricMorophenyl)-3-oxo-propionitrile sodium salt To a solution of sodium ethoxide (NaOEt) (from 0.803g of sodium) in ethanol (55ml) cooled in ice, under nitrogen, was added 2,3,5-trichlorophenyl acetonitrile. Ethyl formate (5.1ml) was added and the mixture was stirred at room temperature overnight. After stirring for a further 2.5 hours at 50°C, the mixture was cooled and filtered. The filtrate was evaporated, and the residue was titurated with diethyl ether, filtered and dried (6.82g). (v) Preparation of 2-f 2.3.5-trichlorophenylV3 -methoxy-acrylonitrile The above solid was dissolved in DMF (36ml) and methyliodide (2ml) was added. The reaction vessel was sealed before stirring the contents at 40°C for 3 hours. The solvent was then evaporated. The residue was partitioned between water and ethyl acetate. The organic phase was washed with water, dried (MgSO4) and the solvent evaporated to give the crude product as a red-brown oil that solidified on standing (5.04g). (vi) Preparation of 4-amino-2-(4-methylpiperazine-l-yl)-5-f2.3.5- trichlorophenyDpyrimidine To a solution of NaOEt (from 0.2g of sodium) in ethanol (20ml) was added N- methylpiperazinoformamidine hydriodide (2.06g) (Example 2). After stirring for a further 10 minutes, the 2-(2,3,5-trichlorophenyl)-3-methoxy-acrylonitrile was added and the mixture was stirred at reflux for 4 hours. The mixture was left standing at room temperature overnight and then filtered. The filtrate was concentrated and the residue was purified by chromatography on Siθ2, eluting with CHCI3 to 4% MeOH CHCl3 to give the title compound as the free base, 0.89g, mp. 162-164°C. The free base (0.805g) was then dissolved in ethanol (35ml) and cooled in an ice bath. Methanesulphonic acid (0.21g) was added and the reaction was stirred at room temperature for 2 hours. The solvent was then evaporated and the residue was triturated with diethyl ether, filtered, dissolved in cold water and freeze dried to give the title salt as a pale green solid, 0.98g, mp. 143-146°C. 1 H MR data (δ), dimethylsulphoxide (DMSO)-d 6 : 7.8(d,lH), 7.65(s,lH), 7.36(d,lH), 6.33-6.23(brs,2H), 3.68(t,4H), 2.32(t,4H), 2.2(s,3H). In the foregoing, the signals have been abbreviated as follows: s = singlet; d = doublet; t = triplet; brs = broad singlet. Example 4 (i) Preparation of methylthiouronium iodide Thiourea (10.89g) was dissolved in acetone (250ml) at 50°C. Iodomethane (10ml) was added and the reaction was stirred at 50°C for 4 hours. After cooling, the solution was diluted with ether (1 litre) and the methiodide salt was filtered, washed with ether and dried in vacuo. 29.2g, mp. 113-115°C. (ii) Preparation of 4- Amino-2-(4-n-propylpiperazine-l-ylV5- 2.3.5- trichlorophenyDpyrimidine dimesylate N-propylpiperazine dihydrobromide (Lancaster 5g) in water (15ml) was passed onto an ion exchange column (IR410 OH form) (BDH) and eluted with water. The eluate that was positive for secondary amine was concentrated, dissolved in diethylether, dried (MgSO4) and evaporated to dryness to give n-propylpiperazine as a colourless oil (0-6g). The piperazine was dissolved in water (10ml) and methylthiouronium iodide added. The solution was stirred, with nitrogen bubbled through, at room temperated for 96 hours. The solution was concentrated in vacuo. The residue was slurried with acetone, filtered and dried in vacuo to give N-propylpiperazinoformamidine hydroiodide, 0.5 lg, mp. 174- 176°C. To a solution of NaOEt (from 0.52g of sodium) in ethanol (5ml) was added N- propylpiperazmofo-rmamidine hydroiodide 0.506g). After stirring for a further 10 minutes, the 2-(2,3,5-trichlorophenyl)-3-methoxy-acrylonitrile of Reference Example 3(v) (0.226g) was added and the mixture was stirred at reflux for 5 hours. The mixture was concentrated, dissolved in chloroform and filtered. The filtrate was reconcentrated and the residue was purified by chromatography on SiO 2 , eluting with 5% MeOH/CHCl3 to give the title compound as the free base. 0.26g. The free base (0.26g) was dissolved in Et 2 O and cooled in an ice bath. Methanesulphonic acid (0.062g) was added and the reaction was stirred in the ice bath for 1 hour. The solid was filtered and dried in vacuo to give the title salt as a yellow amorphous solid, 0.21g, dec. 83°C. NMR Assignment (δ) Solvent - DMSO δ 0.95(t,3H), δ 1.75(m,2H), δ 2.35(s,6H), δ 3.10(d,br,2H), δ 3.40(t,br,4H), δ 3.60(d,br, 2H), δ 4.60(d,2H), δ 7.45(d,lH), δ 7.90(s,lH), δ 7.95(d,lH).

Claims: CLAIMS 1. A process of preparing 2, 3, 5 -trihalobenzaldehyde, which comprises the steps of (i) reacting a compound of formula (I): wherein Hal is halogen, with a di-Cι_4 alkylformamide; (ii) allowing the resulting complex to rearrange; and (ϋi) quenching the rearranged complex with water. 2. A process according to claim 1, wherein halogen is chloro. 3. A process according to claim 1 or 2, wherein the di-Cι_4 alkylformamide is dimethylformamide. 4. A process according to any of the preceding claims, wherein step (i) is carried out at a temperature of from -20 to -80°C 5. A process according to any of the preceding claims, wherein step (ii) is carried out over a period from 2 to 24 hours. 6. A process according to any of the preceding claims, wherein step (ii) is carried out at a temperature of from 15 to 35 °C. 7. A process according to claim 1, wherein the compound of formula (I) is prepared by reacting 2,2,4-trihalobenzene with C\_$ alkyllithium. 8. A process according to claim 7, wherein the molar ratio of Cj_4 alkyllithium to di Cι_4 alkylformamide is 1 : 5.45. 9. A process according to claim 7 or 8, wherein the C . alkyllithium is methyllithium or n-butyllithium. 10. Use of a 2, 3, 5-trihalobenzaldehyde prepared in accordance with any of the preceding claims in the chemical synthesis of 4-amino-2-(4-methylpiperazin-l-yl)- 5-(2, 3, 5-trihalophenyl) pyrimidine or 4-amino-2-(4-n-propylpiperazin-l-yl)-5- (2,3,5-trihalophenyl) pyrimidine. 11. Use of a 2,3,5 trihalobenzaldehyde according to claim 9, wherein halo is chloro.

Inventors: BARRAS JAMES ROBERT, GERMAIN ANDREW LAWRENCE, MILNE DAVID JOHN, PACKHAM TERENCE WILLIAM, PATEL RAJNIKANT, BARRAS, JAMES, ROBERT, GERMAIN, ANDREW, LAWRENCE, MILNE, DAVID, JOHN, PACKHAM, TERENCE, WILLIAM, PATEL, RAJNIKANT
Applicants: BARRAS JAMES ROBERT, GERMAIN ANDREW LAWRENCE, MILNE DAVID JOHN, PACKHAM TERENCE WILLIAM, PATEL RAJNIKANT, WELLCOME FOUND, BARRAS, JAMES, ROBERT, GERMAIN, ANDREW, LAWRENCE, MILNE, DAVID, JOHN, PACKHAM, TERENCE, WILLIAM, PATEL, RAJNIKANT, THE WELLCOME FOUNDATION LIMITED
Application year: 1994
Main classification: C07C45
IPC codes: C07C17, C07C29, C07C33, C07C45, C07C47, C07D239, C07D295